1. Field of the Invention
The present invention relates to an oscillator and a mixer applied to a television tuner performing wide band reception etc.
2. Description of the Related Art
First, an explanation will be made of a related art referring to the drawings.
FIG. 1 is a system block diagram of a usual television tuner circuit for UHF/VHF.
In FIG. 1, ANT denotes a UHF/VHF antenna; STC.sub.U a UHF single-tuned circuit; STC.sub.VH a VHF "High" single-tuned circuit; STC.sub.VL a VHF "Low" single-tuned circuit; AMP.sub.U a UHF RF amplifier; AMP.sub.V a VHF RF amplifier; DTC.sub.U a UHF double-tuned circuit; DTC.sub.VH and DTC.sub.LH VHF double-tuned circuits; and IC an integrated frequency conversion circuit.
In a VHF operation mode, where the VHF broadcast is received, the television signal received via the antenna ATN is input to single-tuned circuits STC.sub.VH and STC.sub.VL. In the single-tuned circuits STC.sub.VH and STC.sub.VL, the input television signal is tuned to the frequency of the desired channel and input to the RF amplifier AMP.sub.V. The RF amplifier AMP.sub.V is constituted by for example a dual gate MOS FET (metal oxide semiconductor field effect transistor), the outputs of the single-tuned circuits STC.sub.VH and STC.sub.VL are output to one gate, an AGC voltage is input to the other gate, and the high frequency output is extracted. The high frequency output of the RF amplifier AMP.sub.V is subjected to a predetermined tuning function by the double-tuned circuits DTC.sub.VH and DTC.sub.VL, and then input to the mixing circuit MIX.sub.V of the integrated frequency conversion circuit IC. In the mixing circuit MIX.sub.V, mixing with the local oscillation frequency signal S.sub.LV by the local oscillation circuit OSC.sub.V having a frequency higher than the frequency of a video image carrier wave signal RF.sub.V of the selected channel by a predetermined frequency is carried out, so that an intermediate frequency signal IF.sub.V which is the frequency of a difference thereof is extracted. This is output to the IF amplifier AMP.sub.IF commonly used for UHF and VHF. In the IF amplifier AMP.sub.IF, the predetermined amplification function is carried out, so that the IF output of VHF is obtained.
In a UHF operation mode, when a UHF broadcast is received, the television signal of the UHF band received via the antenna ATN is input to the single-tuned circuit STC.sub.U. In the single-tuned circuit STC.sub.U, the input television signal is tuned to the frequency of the desired channel and input to the RF amplifier AMP.sub.U. The RF amplifier AMP.sub.U is constituted by for example the dual gate MOS FET. TO one gate is input the output of the single-tuned circuit STC.sub.U, and to the other gate is input the AGC voltage, so that the high frequency output is extracted. The high level frequency output of the RF amplifier AMP.sub.V is subjected to the predetermined tuning function by the double-tuned circuit DTC.sub.U, then input to the mixing circuit MIX.sub.U of the integrated frequency conversion circuit IC. In the mixing circuit MIX.sub.U, mixing with the local oscillation frequency signal S.sub.LU by the local oscillation circuit OSC.sub.U having a frequency higher than the video image carrier wave frequency of the selected channel by a predetermined frequency is carried out, so that an intermediate frequency signal IF.sub.U which is the frequency of the difference thereof is extracted. This is output to the IF amplifier AMP.sub.IF, commonly used for UHF and VHF. In the IF amplifier AMP.sub.IF, the predetermined amplification function is carried out, so that the IF output of UHF is obtained.
The integrated frequency conversion circuit IC is constituted by a VHF circuit of a VHF local oscillation circuit OSC.sub.V and a mixing circuit MIX.sub.V thereof, a UHF circuit of a UHF local oscillation circuit OSC.sub.U and a mixing circuit MIX.sub.U thereof, and an IF amplifier AMP.sub.IF which amplifies an intermediate frequency signal IF.sub.V from the VHF mixing circuit MIX.sub.V and an intermediate frequency signal IF.sub.U from the UHF mixing circuit MIX.sub.U.
In the integrated frequency conversion circuit IC in the above-mentioned tuning circuit, to achieve a reduction of consumption of electric power and simplify a circuit construction, the IF amplifier AMP.sub.IF is used in common, and therefore the VHF circuit of the VHF local oscillation circuit OSC.sub.V and the mixing circuit MIX.sub.V, and the UHF circuit of the UHF local oscillation circuit OSC.sub.U and the mixing circuit MIX.sub.U are selectively operated in accordance with either the VHF or UHF mode. More specifically, a UHF/VHF mode changing signal (not shown) is input to the integrated frequency conversion circuit IC from an outside control system to drive a switching circuit (not shown), whereby current sources for driving the respective circuit in the UHF circuit or the respective circuit in the VHF circuit are turned ON or OFF.
An explanation will be made below of a concrete circuit structure of a general VHF local oscillation circuit OSC.sub.V, UHF local oscillation circuit OSC.sub.U, switching circuit, a VHF mixing circuit MIX.sub.V, and a UHF mixing circuit MIX.sub.U in the integrated frequency conversion circuit IC with reference to FIG. 2 to FIG. 4.
FIG. 2 is a circuit diagram showing an example of the circuit configuration of a VHF local oscillation circuit OSC.sub.V and an output buffer thereof. OSC.sub.V denotes a VHF local oscillation circuit; RSN an external variable resonance circuit; and BUF.sub.V an output buffer, respectively.
The VHF local oscillation circuit OSC.sub.V and the output buffer BUF.sub.V are integrated. The VHF local oscillation circuit OSC.sub.V is connected via three input/output terminals T.sub.1 to T.sub.3, which are connection terminals for an external circuit etc., to the external variable resonance circuit RSN.sub.V.
The VHF local oscillation circuit OSC.sub.V is constituted as a positive feedback differential amplifier type oscillation circuit, consisting of npn-type transistors Q.sub.1 and Q.sub.2 functioning as an oscillator, a constant voltage source V.sub.1 for biasing the npn-type transistors Q.sub.1 and Q.sub.2, resistance elements R.sub.1, R.sub.2, and R.sub.3, and a constant current source I.sub.1.
The base of the oscillation transistor Q.sub.1 is connected to the input/output terminal T.sub.1, connected via the resistance element R.sub.1 to the constant voltage source V.sub.1, and further connected to the base of the npn-type transistor Q.sub.4 of the output buffer BUF.sub.V. The emitter of the oscillation transistor Q.sub.1 is connected to the constant current source I.sub.1, and another terminal of the constant current source I.sub.1 is grounded. The collector of the oscillation transistor Q.sub.1 is connected to a line feeding a power source voltage V.sub.CC.
The base of the oscillation transistor Q.sub.2 is connected to the input/output terminal T.sub.3, connected via the resistance element R.sub.2 to the constant voltage source V.sub.1 and further connected to the base of the npn-type transistor Q.sub.3 of the output buffer BUF.sub.V. The emitter of the oscillation transistor Q.sub.2 is connected to the constant current source I.sub.1 and the collector thereof is connected to the input/output terminal T.sub.2. Also, the resistance element R.sub.3 is connected between the line of the power source voltage V.sub.CC and the collector of the oscillation transistor Q.sub.2.
The external variable resonance circuit RSN.sub.1 is constituted by a variable capacitance capacitor CV.sub.1 and a coil L.sub.2 which are connected in parallel. A connection point of one end of the coil L.sub.2 of the external variable resonance circuit RSN.sub.1 and one electrode of the variable capacitance capacitor CV.sub.1 is grounded. A connection point of the other end of the coil L.sub.2 and the other electrode of the variable capacitance capacitor CV.sub.1 is connected via the capacitor C.sub.1 and the input/output terminal T.sub.1 to the base of the oscillation transistor Q.sub.1, and connected via the capacitor C.sub.2 and the input/output terminal T.sub.2 to the collector of the oscillation transistor Q.sub.2. Also, one electrode of a capacitor C.sub.3 is connected to an input/output terminal T.sub.3, and the other electrode of the capacitor C.sub.3 is grounded.
The VHF local oscillation circuit OSC.sub.V is subjected to a positive feedback of the externally attached capacitor C.sub.1 connected via the input/output terminals T.sub.1 and T.sub.2 to the base of the oscillation transistor Q.sub.1. It oscillates at the resonance frequency of the external variable resonance circuit RSN.sub.1 and outputs the resonance signal to the output buffer BUF.sub.V.
The output buffer BUF.sub.V is constituted by npn-type transistors Q.sub.3 and Q.sub.4, resistance elements R.sub.5 to R.sub.7 functioning as load resistor, resistance elements R.sub.8 to R.sub.11, and the constant current source I.sub.2.
The base of the transistor Q.sub.3 is connected to the base of the oscillation transistor Q.sub.2 of the local oscillation circuit OSC.sub.V as mentioned above, the emitter is connected via the resistance elements R.sub.8 and R.sub.9, connected in series, to the constant current source I.sub.2, and another terminal of the constant current source I.sub.2 is grounded. The collector of the transistor Q.sub.3 is connected via the series-connected load resistance elements R.sub.6 and R.sub.5 to the line of the power source voltage V.sub.CC.
Note that, the output terminal O.sub.UT1V of the local oscillation circuit for VHF is constituted by the connection point of the resistance element R.sub.8 and the resistance element R.sub.9. This output terminal O.sub.UT1V is connected to the integrated VHF mixing circuit MIX.sub.V in FIG. 1.
The base of the transistor Q.sub.4 is connected to the base of the oscillation transistor Q.sub.1 of the local oscillation circuit OSC.sub.V as mentioned above, and the emitter is connected via series-connected resistance elements R.sub.10 and R.sub.11 to the constant current source I.sub.2. The collector of the transistor Q.sub.4 is connected via the load resistance element R.sub.7 to the connection point of the series-connected load resistance elements R.sub.7 and R.sub.5.
Note that the output terminal O.sub.UT2V of the VHF local oscillation circuit OSC.sub.V is constituted by the connection point of the resistance element R.sub.10 and the resistance element R.sub.11. This output terminal O.sub.UT2V is connected to the integrated VHF mixing circuit MIX.sub.V in FIG. 1.
FIG. 3 is a circuit diagram showing one example of the configuration of the UHF local oscillation circuit OSC.sub.U and switching circuit. In FIG. 3, OSC.sub.U denotes a UHF local oscillation circuit; SW denotes a switching circuit; and an RSN.sub.2 denotes an external variable resonance circuit, respectively.
The UHF local oscillation circuit OSC.sub.U and the switching circuit SW are integrated. The UHF local oscillation circuit OSC.sub.U is connected via four input/output terminals T.sub.5 to T.sub.8, which are connection terminals to an external circuit etc., to the external variable resonance circuit RSN.sub.2.
Also, a UHF/VHF mode changing signal S.sub.SW is applied to the switching circuit SW via the switching terminal T.sub.4 provided separately from the input/output terminals T.sub.5 to T.sub.8.
The UHF local oscillation circuit OSC.sub.U is constituted by a differential operation type Colpitz oscillation circuit, consisting of npn-type transistors Q.sub.7 and Q.sub.8 used for oscillation, a constant voltage source V.sub.2 biasing the oscillation non-type transistors Q.sub.7 and Q.sub.8, resistance elements R.sub.13 and R.sub.14, resistance elements R.sub.15 and R.sub.16 functioning as load resistors of the oscillation npn-type transistors Q.sub.7 and Q.sub.8, and constant current sources I.sub.3 and I.sub.4.
The base of the oscillation transistor Q.sub.7 is connected to the input/output terminal T.sub.5 and, connected via the resistance element R.sub.13 to the constant voltage source V.sub.2. The emitter of the oscillation transistor Q.sub.1 is connected to the input/output terminal T.sub.6 and connected to the constant current source I.sub.3, and the other terminal of the constant current source I.sub.3 is grounded. The collector of the oscillation transistor Q.sub.7 is connected via the load resistance element R.sub.15 to the line of the power source voltage V.sub.CC, and the output terminal O.sub.UT1U of the differential operation type Colpitz oscillation circuit is constituted by the connection point of the collector of the oscillation transistor Q.sub.7 and the load resistance element R.sub.15. This output terminal O.sub.UT1U is connected to the integrated mixing circuit MIX.sub.U in FIG. 1.
The base of the oscillation transistor Q.sub.8, is connected to the input/output terminal T.sub.8, and connected via the resistance element R.sub.14 to the constant voltage source V.sub.2. The emitter of the oscillation transistor Q.sub.8 is connected to the input/output terminal T.sub.7 and connected to the constant current source I.sub.4, and the other terminal of the constant current source I.sub.4 is grounded. The collector of the oscillation transistor Q.sub.8, is connected via the load resistance element R.sub.16 to the line of the power source voltage V.sub.CC, and the output terminal O.sub.UT2U of the differential operation type Colpitz oscillation circuit is constituted by the connection point of the collector of the oscillation transistor Q.sub.8, and the load resistance element R.sub.16. This output terminal O.sub.UT2U is connected to the integrated mixing circuit MIX.sub.U.
The external variable resonance circuit RSN.sub.2 is constituted by connecting a capacitor C.sub.5 in parallel to the serial circuit of a variable capacitance capacitor CV.sub.2 and a coil L.sub.3. The connection point of the coil L.sub.3 of the external variable resonance circuit RSN.sub.2 and the capacitor C.sub.5 is connected via a DC cutting capacitor C.sub.6 and the input/output terminal T.sub.5 to the base of the oscillation transistor Q.sub.7, and the connection point of an anode of the variable capacitance diode CV.sub.2 and the capacitor C.sub.5 is connected via the DC cutting capacitor C.sub.7 and the input/output terminal T.sub.8 to the base of the oscillation transistor Q.sub.8.
Also, a positive feedback capacitor C.sub.8 is connected between the connection point of the capacitor C.sub.6 and input/output terminal T.sub.5 and the input/output terminal T.sub.6, and a positive feedback capacitor C.sub.9, is connected between the connection point of the capacitor C.sub.7 and input/output terminal T.sub.8, and the input/output terminal T.sub.7.
Further, a coupling capacitor C.sub.10 is connected to the connection point of the capacitor C.sub.8 and the input/output terminal T.sub.6 and the connection point of the capacitor C.sub.9 and the input/output terminal T.sub.7, i.e., between the emitter of the oscillation transistor C.sub.5 and the emitter of the oscillation transistor Q.sub.8. The UHF local oscillation circuit OSC.sub.U is subjected to a positive feedback of the externally attached capacitors C.sub.8 and C.sub.9 connected to the base and emitter of the oscillation transistors Q.sub.7 and Q.sub.8 via the input/output terminals T.sub.5, T.sub.6, T.sub.7, and T.sub.8. It oscillates by the resonance frequency of the external variable resonance circuit RSN.sub.2 connected to the respective bases of the oscillation transistors Q.sub.7 and Q.sub.8 and outputs a local oscillation frequency signal S.sub.LU having a predetermined frequency from the output terminals O.sub.UT1U and O.sub.UT2U to the UHF mixing circuit MIX.sub.U.
Note that, the oscillation transistors Q.sub.7 and Q.sub.8 constituting the differential operation type Colpitz oscillation circuit are mutually connected at their respective bases via the external variable resonance circuit RSN.sub.2 and therefore perform oscillation operations of out of phases. Accordingly, local oscillation frequency signals S.sub.LU having out of phases to each other are output from the output terminals O.sub.UT1T and O.sub.UT2U.
The switching circuit SW is constituted by the switching operation npn-type transistors Q.sub.5 and Q.sub.6 and resistance elements R.sub.18, R.sub.19, and R.sub.20.
The base of the switching transistor Q.sub.5 is connected via the resistance element R.sub.18 to the collector of the switching transistor Q.sub.6, the emitter thereof is grounded, and the collector is connected to the not illustrated UHF system current source. The base of the switching transistor Q.sub.6 is connected via the resistor R.sub.20 to the switching terminal T.sub.4, the emitter thereof is grounded, the connection point of the collector and the resistance element R.sub.18 is connected via a high resistance element R.sub.19 to the line of the power source voltage V.sub.CC, and the connection point of the collector and the resistance element R.sub.18 and the connection point with the high resistance element R.sub.19 is connected to the not illustrated VHF system current source.
FIG. 4 is a circuit diagram showing an example of the circuit configuration of the VHF mixing circuit MIX.sub.V and the UHF mixing circuit MIX.sub.U. These circuits are integrated.
The VHF mixing circuit MIX.sub.V is constituted by npn-type transistors Q.sub.11 to Q.sub.16, resistance elements R.sub.21 to R.sub.23, and constant current sources I.sub.6 and I.sub.7.
The base of the transistor Q.sub.11 is connected to the output of the VHF local oscillation circuit OSC.sub.V and the base of the transistor Q.sub.14. The emitter of the transistor Q.sub.11 is connected to the emitter of the transistor Q.sub.12 and the collector of the transistor Q.sub.15. The collector of the transistor Q.sub.11 is connected via the resistance element R.sub.21 to the line of the power source voltage V.sub.CC, and the connection point of the collector and the resistance element R.sub.21 is connected to one input of the IF amplifier AMP.sub.IF.
The base of the transistor Q12.sub.V is connected to the output of the VHF local oscillation circuit OSC.sub.V and the base of the transistor Q.sub.13, and the collector is connected to the other input of the IF amplifier AMP.sub.IF.
The emitter of the transistor Q.sub.13 is connected to the emitter of the transistor Q.sub.14 and the collector of the transistor Q.sub.16. The collector of the transistor Q.sub.13 is connected to the one input of the IF amplifier AMP.sub.IF.
The collector of the transistor Q.sub.14 is connected via the resistance element R.sub.22 to the line of the power source voltage V.sub.CC, while the connection point of the collector and the resistance element R.sub.22 is connected to the other input of the IF amplifier AMP.sub.IF.
The base of the transistor Q.sub.15 is connected to the output of the double-tuned circuits DTC.sub.VH and DTC.sub.VL shown in FIG. 1, the emitter is connected to the constant current source I.sub.6, and the constant current source I.sub.6 is grounded.
The base of the transistor Q.sub.16 is connected to the output of the double-tuned circuits DTC.sub.VH and DTC.sub.VL shown in FIG. 1, the emitter is connected to the constant current source I.sub.7, and the constant current source I.sub.7 is grounded.
Also, a resistance element R.sub.23 is connected between the emitter of the transistor Q.sub.15 and the emitter of the transistor Q.sub.16. This VHF mixing circuit MIX.sub.V mixes the local oscillation frequency signal S.sub.LV by the local oscillation circuit OSC.sub.V having a frequency higher than the frequency of a video image carrier wave signal RF.sub.V of the selected channel by a predetermined frequency, for example, 58.75 MHz, extracts an intermediate frequency signal IF.sub.V which is the frequency of a difference thereof, and outputs the same to the IF amplifier AMP.sub.IF, commonly used for UHF and VHF.
The UHF mixing circuit MIX.sub.U is constituted by npn-type transistors Q.sub.18 to Q.sub.24, resistance elements R.sub.24 to R.sub.26, and constant current sources I.sub.8 and 1.sub.9.
The base of the transistor Q.sub.18 is connected to the output of the UHF local oscillation circuit OSC.sub.U and the base of the transistor Q.sub.22. The emitter of the transistor Q.sub.18 is connected to the emitter of the transistor Q.sub.19 and the collector of the transistor Q.sub.23. The collector of the transistor Q.sub.18 is connected via the resistance element R.sub.24 to the line of the power source voltage V.sub.CC, and the connection point of the collector and the resistance element R.sub.24 is connected to one input of the IF amplifier AMP.sub.IF.
The base of the transistor Q.sub.19 is connected to the output of the UHF local oscillation circuit OSC.sub.U and the base of the transistor Q.sub.21, and the collector is connected to the other input of the IF amplifier AMP.sub.IF.
The emitter of the transistor Q.sub.21 is connected to the emitter of the transistor Q.sub.22 and the collector of the transistor Q.sub.24. The collector of the transistor Q.sub.21 is connected to one input of the IF amplifier AMP.sub.IF.
The collector of the transistor Q.sub.22 is connected via the resistance element R.sub.25 to the line of the power source voltage V.sub.CC, and the connection point of the collector and the resistance element R.sub.25 is connected to the other input of the IF amplifier AMP.sub.IF.
The base of the transistor Q.sub.23 is connected to the output of the double-tuned circuit DTC.sub.U shown in FIG. 1, the emitter thereof is connected to the constant current source I.sub.8, and the other terminal of the constant current source I.sub.8 is grounded.
The base of the transistor Q.sub.24 is connected to the output of the double-tuned circuit DTC.sub.U shown in FIG. 1, the emitter thereof is connected to the constant current source I.sub.9, and other terminal of the constant current source I.sub.9 is grounded.
Also, a resistance element R.sub.26 is connected between the emitter of the transistor Q.sub.23 and the emitter of the transistor Q.sub.24. This UHF mixing circuit MIX.sub.U mixes the local oscillation frequency signal S.sub.LU by the local oscillation circuit OSC.sub.U having a frequency higher than the frequency of a video image carrier wave signal RF.sub.U of the selected channel by predetermined frequency, for example, 58.75 MHz, extracts an intermediate frequency signal IF.sub.U which is the frequency of a difference thereof, and outputs the same to the IF amplifier AMP.sub.IF commonly used for UHF and VHF.
In such a structure, at the VHF operation, the UHF/VHF mode changing signal S.sub.SW of a low level "0 V" is input to the switching terminal T.sub.4 by for example the external control system. Alternatively, the switching terminal T.sub.4 is opened. By this, the base potential of the switching transistor Q.sub.6 becomes "0 V", and therefore the switching transistor Q.sub.6 is retained to the OFF state. Accordingly, a current generated via the high resistance element R.sub.19 is supplied to the current source for VHF. Along with this, a driving current is supplied to the VHF mixing circuit MIX.sub.V and local oscillation circuit OSC.sub.V. Also, a current generated via the high resistance element R.sub.19 is applied via the resistance element R.sub.18, as the predetermined signal voltage to the base of the switching transistor Q.sub.5. By this, the switching transistor Q.sub.5 becomes the ON state, and the UHF system current source connected to the collector thereof is turned OFF. Accordingly, the driving current is not supplied to the UHF mixing circuit MIX.sub.U and local oscillation circuit OSC.sub.U.
In such a VHF operation mode, where the VHF broadcast is received, the television signal received via the antenna ATN is input to single-tuned circuits STC.sub.VH and STC.sub.VL. In the single-tuned circuits STC.sub.VH and STC.sub.VL, the input television signal is tuned to the frequency of the desired channel and input to the RF amplifier AMP.sub.V. The RF amplifier AMP.sub.V is constituted by for example a dual gate MOS FET, the outputs of the single-tuned circuits STC.sub.VH and STC.sub.VL are output to one gate, an AGC voltage is input to the other gate, and the high frequency output is extracted. The high frequency output of the RF amplifier AMP.sub.V is subjected to a predetermined tuning function by the double-tuned circuits DTC.sub.VH and DTC.sub.VL, and then input to the mixing circuit MIX.sub.V of the integrated frequency conversion circuit IC. In the mixing circuit MIX.sub.V, mixing with the local oscillation frequency signal S.sub.LV by the local oscillation circuit OSC.sub.V having a frequency higher than the frequency of a video image carrier wave signal RF.sub.V of the selected channel by a predetermined frequency is carried out, so that an intermediate frequency signal IF.sub.V which is the frequency of a difference thereof is extracted. This is output to the IF amplifier AMP.sub.IF commonly used for UHF and VHF. In the IF amplifier AMP.sub.IF, the predetermined amplification function is carried out, so that the IF output of VHF is obtained.
Contrary to this, in a UHF operation, a UHF/VHF mode changing signal S.sub.SW of a high level "9 V" the same level as that of the power source voltage V.sub.CC is applied to the switching terminal T.sub.SW by for example the external control system. By this, the base potential of the switching transistor Q.sub.6 becomes the high level, and therefore the switching transistor Q.sub.6 is retained in the ON state. Accordingly, a current generated via the high resistance element R.sub.19 flows through the switching transistor Q.sub.6, not supplied to the VHF current source, and the collector side is held at "0 V" at the switching transistor Q.sub.6. Along with this, the driving current is not supplied to the VHF mixing circuit MIX.sub.V and local oscillation circuit OSC.sub.V. Also, the collector side of the switching transistor Q.sub.6 is retained at "0 V", and therefore the base terminal of the switching transistor Q.sub.5 becomes "0 V", whereby the switching transistor Q.sub.5 is retained in the OFF state. By this, the UHF system current source connected to the collector of the switching transistor Q.sub.5 becomes ON. Accordingly, the driving current is supplied to the UHF mixing circuit MIX.sub.U and local oscillation circuit OSC.sub.U.
In such a UHF operation mode, when a UHF broadcast is received, the television signal of the UHF band received via the antenna ATN is input to the single-tuned circuit STC.sub.U. In the single-tuned circuit STC.sub.U, the input television signal is tuned to the frequency of the desired channel and input to the RF amplifier AMP.sub.U. The RF amplifier AMP.sub.U is constituted by for example the dual gate MOS FET. To one gate is input the output of the single-tuned circuit STC.sub.U, and to the other gate is input the AGC voltage, so that the high frequency output is extracted. The high level frequency output of the RF amplifier AMP.sub.V is subjected to the predetermined tuning function by the double-tuned circuit DTC.sub.U, then input to the mixing circuit MIX.sub.U of the integrated frequency conversion circuit IC. In the mixing circuit MIX.sub.U, mixing with the local oscillation frequency signal S.sub.LU by the local oscillation circuit OSC.sub.U having a frequency higher than the video image carrier wave frequency of the selected channel by a predetermined frequency is carried out, so that an intermediate frequency signal IF.sub.U which is the frequency of the difference thereof is extracted. This is output to the IF amplifier AMP.sub.IF commonly used for UHF and VHF. In the IF amplifier AMP.sub.IF, the predetermined amplification function is carried out, so that the IF output of UHF is obtained.
As in the above, in the conventional circuit, a single terminal has been used as the UHF/VHF mode changing terminal T.sub.SW.
A television tuner etc. handles high frequency signals, and therefore the wiring of the wiring pattern exerts a great influence upon the characteristics.
Also, in an integrated frequency conversion circuit IC comprising integrated mixing circuits MIX.sub.V and MIX.sub.U, local oscillation circuits OSC.sub.V and OSC.sub.U, and the IF amplifier AMP.sub.IF, when the package becomes large and the inner lead portion from the bare chip to the outside becomes long, there arises problems of a parasitic oscillation and a lowering of the gain due to its parasitic inductance and parasitic capacitance.
Accordingly, an integrated circuit IC for a tuner desirably has as small number of terminals as possible and is accommodated in a small package.
In the above-mentioned conventional circuit of FIG. 3, however, the UHF/VHF mode changing terminal T.sub.SW is provided independently besides the four terminals T.sub.5 to T.sub.8 for the connection with the external variable resonance circuit RSN of the local oscillation circuit OSC.sub.U, and therefore an increase of the number of terminals is caused and also the package size becomes large. For this reason, there are problems of the parasitic oscillation and lowering of gain, and consequently a defect that the enlargement of the size of the tuner and an increase of the costs are induced.
For the reduction of the number of terminals, usually it can be considered to use the three terminals used for the VHF local oscillation circuit OSC.sub.V and the UHF local oscillation circuit OSC.sub.U, but the UHF local oscillation circuit has a high operation frequency, and therefore a differential operation type oscillation circuit is preferable for a stable operation.
In a television tuner etc., the UHF local oscillation circuit has a high operation frequency, and therefore for a stable operation, a differential operation type Colpitz oscillation circuit as shown in FIG. 3 has been used as an oscillator which can stably oscillate over a wide band width.
Accordingly, the four terminals T.sub.5 to T.sub.8 for the connection with the external variable resonance circuit RSN.sub.2 cannot be reduced.
Recently, in a television tuner or mobile radio frequency receiver handling a relatively high frequency signal such as an UHF band or submicrowave band, a further higher stability local oscillator has been required.
So as to satisfy this request, generally there is adopted a method of locking the frequency using for example a PLL (phase locked loop) circuit. As the oscillator used for this, in the frequency conversion circuit of for example a television tuner, a so-called two-output type is ideally used, which can perform output to both of the PLL circuit and the mixing circuit. In the above-mentioned conventional oscillator, however, one oscillation signal output is used for input to the mixing circuit, and therefore the application thereof to locking the frequency using the PLL circuit is difficult.
Here, a case where both of the mixing circuit and the PLL circuit are driven by one oscillation signal output is considered. The mixing circuit and the PLL circuit have optimum input levels, respectively, and therefore a circuit for controlling the level becomes necessary for either of the mixing circuit or the PLL circuit, so that there arises a problem that the circuit becomes complex etc.
Also, when taking a television tuner as an example, the RF signal is input to the mixing circuit in addition to the output of the local oscillator, but where this RF signal is input with a great oscillation width, there is a concern that it will pass the mixing circuit and enter into the PLL circuit. In this case, there is a possibility of a malfunction of the PLL circuit due to the RF signal. For this reason, it must be separated so that the signal is not leaked from the mixing circuit to the PLL circuit. This is cumbersome.
Also, as a method of stably extracting a plurality of oscillation signal outputs, there can be considered a configuration in which a so-called emitter follower EF is added to the output of the oscillator OSC, a configuration in which the buffer amplifier BF is added to the output of the oscillator OSC, or a configuration in which the transistors are connected in cascade. Note that, the loads of the oscillation transistors Q.sub.1 and Q.sub.3 can be constituted using diodes D.sub.1 and D.sub.2.
However, the configuration of loading the emitter follower EF and the configuration of adding the buffer amplifier BF involve the problem of an increase of the consumed electric current.
In the configuration of connecting the transistors in cascade, one level's worth of an excess application voltage is necessary, and therefore it is not suitable for the lowering of voltage. Particularly, when the number of the outputs is increased, there is a defect that the application voltage must be increased by that amount.
Further, in a television tuner, ideally use is made of a so-called two-output type in which output to both of the PLL circuit and mixing circuit is possible.
In the local oscillation circuit used in the conventional integrated frequency conversion circuit IC mentioned above, the VHF local oscillation circuit OSC.sub.V is constituted so as to obtain the oscillation signal output via the output buffer BUF.sub.V, and therefore, in addition to the output from the emitter side of the transistors Q.sub.3 and Q.sub.4 of the output buffer BUF.sub.V to the mixing circuit MIX.sub.V, the oscillation signal output is obtained from the points of connection between the collectors of the transistors Q.sub.3 and Q.sub.4 and the load resistance elements R.sub.6 and R.sub.7. These outputs can be made the outputs to the PLL circuit.
However, in the UHF local oscillation circuit OSC.sub.U, only one oscillation signal output is input to the mixing circuit MIX.sub.U, and therefore application is difficult to locking the frequency using the PLL circuit.
It is also possible to consider a configuration in which a plurality of oscillation transistors constituting a Colpitz oscillation circuit are connected in parallel to obtain a plurality of outputs, and one among them is used for the PLL circuit, but in this case, the number of the output systems to the PLL circuit becomes two, i.e. a signal output from the output buffer BUF.sub.V of the VHF local oscillation circuit OSC.sub.V and a signal output from the UHF local oscillation circuit OSC.sub.U. For inputting an oscillation signal to the PLL circuit basically having one input, it becomes necessary to provide a switching circuit etc., resulting in problems that the connection to the PLL circuit is cumbersome, the number of elements is increased, and so on.
Also, irrespective of the fact that the VHF mixing circuit MIX.sub.V and the UHF mixing circuit MIX.sub.U output the intermediate frequency signals IF.sub.V and IF.sub.U obtained as a result of mixing to the common IF amplifier AMP.sub.IF and, as shown in FIG. 4, both circuits have a similar structure, they are quite separately constituted, and therefore there are problems in that an increase of number of components is induced, and thus the increase of costs and enlargement of size are caused.